2. Function and Operation
Figure 3 illustrates the most important functional groups of M72 in a block diagram.
Figure 3: Block diagram (*these elements only with M72Ax and M72S1)
All functions are controlled by a microcontroller.
Depending on the position of the input switch, the input signal passes the impedance converter
Q1 or Q2. If IEPE operation has been selected, the signal is transmitted to the amplifier via a
buffer stage. During IEPE
operation a constant current is fed into the input socket to supply the
sensor electronics. With the M72Ax and M72S1 instruments the stored electronic data (TEDS)
of selected IEPE sensors can be read out. If an AC voltage supply is to be connected to the in-
put, the constant current supply can be switched off.
The input circuit is followed by the first amplifier stage, low pass and high pass filters. The high
pass filter can be switched between 0.1 Hz and 3 Hz. The low pass filter has 4 frequency limits
to choose from, including 0.1 / 1 / 10 / 50 kHz.
The sensor sensitivity of M72Ax and M72S1 can be entered to achieve finely tuned amplifica-
tion. To aid this there is an adjustable damping stage after the filters.
The single and double integrators can be switched on to measure velocity and displacement, re-
spectively.
A second amplification level follows subsequently. Due to the distributed amplification before
and after the filter there is an overload reserve which is also applied to signal components out -
side of the filter or the integrator pass band. Simultaneously a high signal-to-noise ratio is
achieved.
Before the output socket there is a driving stage with low pass filters to reduce disturbance. The
output is DC coupled.
The overload LED lights up when the output signal is over 90% of the full modulation. It also
signalizes the occurrence of overload before and after the filters and integrators.
The M72Ax and M72S1 instruments have a digital display which shows the modulation at the
output as a percentage of the maximum value.
All settings are configured via the buttons. Five seconds after the last press of a button the in -
strument saves the current settings. This means that the last operating status remains even after
the instrument has been switched off and on again.
The units with display M72Ax and M72S1 show the hardware version and the software version
for one second each, after switching them on.
4
U
Q/10
Q
U
Q/10
Q
Q1
Q2
IEPE
supply
IEPE on/off
L.P. frequency
0,1Hz
3Hz
V2
1. Int.
2. Int.
V1
Gain
a
v
d
Gain
Input
Overload
LED
Output
+
1
TEDS*
Read TEDS
1
10
100
1
10
0,1
1
10
50
kHz
100 kHz
Sensitivity*
0,1...1
Level
indication*
High pass
Low pass
µC